Cargo Bike (Bakfiets) Steering Help

Hi all. Was hoping you could help me out.

TL;DR – I can’t tighten this nut properly and it’s severely impacting my steering. Other possible issues or causes of dodgy steering?

About a year ago I got a second hand Bakfiets.nl cargo bike here in the Netherlands. It was from a guy who refurbishes them and adds a motor, battery etc and the sells on. It was all good for nearly a year aside from a couple of punctures and a quick service I had about 6 months ago to check all ok.

About 6 weeks ago I started having some issues with the steering, it seemed less responsive and there was a horrible creaking noise. I decided to shell out for a rather expensive company to come to my place to give it a full service and they said they oiled a few pieces etc. it felt better but honestly after a couple of weeks the steering felt funny again.

A good summary of my problem is that when walking the bike along I can move the handlebars a significant amount either way without it actually impacting the wheel, the amount of give is making it very difficult to ride.

I’ve tried a few fixes myself like tightening the steering column, adjusting the headsets and evening removing the steering rod and cleaning that. If anything it’s worse than before because I can’t seem to get some nuts on the steering rod to tighten fully, when trying to turn them the whole bolt turns also, see picture. I’ve tried a few things to get a proper grip of it and even taken it off again to ensure it was clean and dry.

A nearby bike shop said one or more bearing could need replacing but he can’t do it for about a week. The company who did the service said there’s no guarantee of service work – despite I feel if there was a possible bigger issue they should have seen it.

So my two questions – how can I get this nut on the steering rod tighter? Do you think there’s a bigger issue like bearings needing replacing or just some decent servicing will alleviate my issues?

Thanks in advance!